Based on an earlier study conducted on rats, the researchers determined that the most efficacious way of testing the specific electrical membrane properties of the non-pyramidal neurons being studied was an application of alternating hyper-polarizing and depolarizing rectangular current pulses lasting five hundred milliseconds (Kawaguchi, 1995, ctd. In Krimer & Goldman-Rakic, 2001). The research confirmed the high firing rates of connected local neurons, especially when compared to the relatively low-firing pyramidal neurons, strengthening the observations of in-tandem functional properties of cortical neurons (Krimer & Goldman-Rakic, 2001). For ease of measurement, voltages were amplified but not altered (Krimer & Goldman-Rakic, 2001).
After conducting the physiological and electronic tests on the prepared neuron pairs, morphological analysis was conducted as well. This was the final step in assessing the differences in conduction of different cortical neurons in relationship to their differences in structure and interrelationship with other neurons; now that electronic measurements had been taken, morphological analysis would provide a more detailed visual picture of the neurons -- specifically the axonal arbors and their proximity to neighboring dendrites -- so that the correlation between the two features could be determined (Krimer & Goldman-Rakic, 2001). This analysis could not be done prior to the recording of electronic conduction data due to the destructive nature of the morphological analysis procedure, which necessarily separated neurons from each other.
The pairs were left intact for one to two hours after the recording process, which allowed enough time for the proper saturation of the neurons with dye to ease visualization of axons, dendrites, and inter-neural spaces (Krimer & Goldman-Rakic, 2001). They were then preserved in a cold paraformaldehyde solution for seventy-two hours before being transferred to an anti-freezing solution and storage at seventy-nine degrees below zero Celsius (Krimer & Goldman-Rakic, 2001). Sections were...
Visual analysis was aided by three-dimensional computer reconstruction (Krimer & Goldman-Rakic, 2001).
The findings and confirmation of other findings that occurred in the process of this research covers a wide area of neurobiological knowledge. The study was undertaken to further understanding of the mechanisms and differentiations in neural functions, specifically cortical functions, and it was a complete success in this goal. The identified differences in postsynaptic interneurons -- specifically, the differences in axonal arbor size and distance -- were shown to have a direct correlation with the number of synapses directly inked to presynaptic pyramidal neurons, suggesting a strong structure-function correlation that increases the efficacy of synaptic and neural functions (Krimer & Goldman-Rakic, 2001). The authors due acknowledge that there were limitations in their methods, specifically when it comes to the area of visual analysis and description of their research samples, but they stress that their findings compare favorably with descriptions of synaptic connections as seen with light microscopes, rather strengthening the reliability of previous data rather than undermining their own methods of measurement and analysis and their own conclusions (Krimer & Goldman-Rakic, 2001).
This research was conducted with a particular interest in the function of cortical neurons in the production and preservation of visual memory, and has significant implications in this area. It had previously been established that mnemonic neurons retain traces of preferred spatial targets and actually appear to be inhibited in the non-preferred direction (Funahashi et al., 1989; Wilson et al., 1994; Rao et al., 1999; ctd. In Krimer & Goldman-Rakic, 2001). Interneurons had long been postulated as the mechanism by which such preference…
